The present invention relates to signal processing, and more particularly, to the processing of signals in the presence of noise.
Signal processing applications often process a signal of interest corrupted with noise. Since noise limits the ability of a circuit or other signal processing system to transmit faithfully the information carried by the signal of interest, it is often desirable to reduce the noise level in a noise corrupted signal.
Filtering is one method of reducing the noise level in a noise corrupted signal. In filtering, the passband of a filter is designed to pass the frequencies associated with the signal of interest and to block or reduce the frequencies not associated with the signal of interest. Unfortunately, noise often contains the same frequencies as the frequencies contained in the signal of interest. In that case, filtering a noise corrupted signal may also distort the signal of interest.
Spectral gain modification is another method of reducing the noise level in a noise corrupted input signal. In applying spectral gain modification to a noise corrupted input signal, the noise corrupted signal is divided into spectral bands, and each spectral band is attenuated according to its signal-to-noise ratio. A spectral band having a high signal-to-noise ratio is attenuated by a small attenuation factor. A spectral band having a low signal-to-noise ratio is attenuated by a large attenuation factor. The spectral bands are then recombined to produce a noise-suppressed output signal. Unfortunately, when spectral gain modification is applied to speech signals, an unwanted side effect occurs. Watery or musical noise, which is characterized by unwanted isolated tones in the speech spectrum, is introduced into the output signal.
For these and other reasons there is a need for the present invention.